DESCRIPTION
The DS1646 is a 128K x 8 nonvolatile static RAM with a full function Real Time Clock (RTC) which are both accessible in a Byte–wide format. The nonvolatile timekeeping RAM is function equivalent to any JEDEC standard 128K x 8 SRAM. The device can also be easily substituted in ROM, EPROM and EEPROM sockets providing read/write nonvolatility and the addition of the real time clock function. The real time clock information resides in the eight uppermost RAM locations. The RTC registers contain year, month, date, day, hours, minutes, and seconds data in 24–hour BCD format. Corrections for the day of the month and leap year are made automatically.

FEATURES
• Integrated NV SRAM, real time clock, crystal, power–fail control circuit and lithium energy source
• Clock registers are accessed identical to the static RAM. These registers are resident in the eight top RAM locations.
• Totally nonvolatile with over 10 years of operation in the absence of power
• Access times of 120 ns and 150 ns
• BCD coded year, month, date, day, hours, minutes, and seconds with leap year compensation valid up to 2100
• Power–fail write protection allows for ±10% VCC power supply tolerance
• DS1646 only (DIP Module)
    – Standard JEDEC Byte–wide 128K x 8 RAM pinout
• DS1646P only (PowerCap Module Board)
    – Surface mountable package for direct connection to PowerCap containing battery and crystal
    – Replaceable battery (PowerCap)
    – Power–fail output
    – Pin–for–pin compatible with other densities of DS164XP Timekeeping RAM